For today's high density magnetic recording, the recorded bits per inch (BPI) and the data rate for writing have both either already entered, or are rapidly approaching, the Giga range. It is essential that this increase in the data rate capability of writers not be accompanied by an increase in the bit error rate (BER).
To enhance the data rate of a writer, its frequency response to the writing current has to be improved. During the writing process, magnetization will follow the Landau-Lifshitz-Gilbert equation:
            ⅆ      M              ⅆ      t        =                    -        γM            ×              H        eff              +                  α        M            ⁢      M      ×                        ⅆ          M                          ⅆ          t                    where M is the magnetization, γ is the gyromagnetic coefficient, Heff is the field, including the applied field, the demagnetization field, and the anisotropic field. α is the Gilbert damping constant. The 1st term is the gyro motion of magnetization around the direction of Heff while the 2nd term is the damping term which will dissipate the energy of M motion and align the M along the direction of Heff.
The value of α determines how fast M aligns with Heff, as illustrated schematically by the two examples shown in FIGS. 1a and 1b. In FIG. 1a α is relatively small while in FIG. 1b α is relatively large. This damping process is a major factor in determining the magnetic material's response time to the writing field. The damping constants of the high saturation magnetization (Ms) materials used in present day writers (Fe, Co, Ni alloys) is small, being in the range of from 0.002 to 0.02.
Another issue facing today's high density writers is the accidental erasure of data due to the remnant magnetization of the write pole. To eliminate this problem, magnetic materials with good soft properties (small anisotropy field Hk) are needed. However, not all soft magnetic materials have an Ms value that is large enough to provide a high intensity writing field.